Last year, Terry Pratchett and Stephen Baxter introduced us to the Long Earth, the system of millions of parallel Earths that can be accessed by “stepping” between worlds, either through an inborn gift or through “stepper boxes” that, once released into the wild, changed everything as humanity discovered that it could leave the Datum Earth for pristine new worlds, as yet untouched by human industry. It was a brilliant piece of multiverse-building, and it’s great to return there with the second book in the series, The Long War.

The Long War picks up ten years after the end of The Long Earth—ten years after Datum Madison, WI was destroyed by a backpack nuke and after Long Earth pioneer and natural stepper Joshua Valienté returned from his exploratory trek. Joshua has settled down and had a son with Helen Green (last seen as a diary-keeping teen, and whose father has now become a leader in Long Earth politics) in the bucolic town of Hell-Knows-Where on Earth West 1,397,426; Sally Linsay continues to traverse the Long Earth and keep her own counsel; and the super-AI known as Lobsang is engaged with various curious projects of its own.

There is unease across the worlds. As the settlements in the distant earths grow increasingly independent, the Datum governments—especially that of the United States—are equally determined to assert their authority. An expedition by US Navy Commander Maggie Kauffman is sent to the Long Earth settlement known as Valhalla, which has lately declared its independence from the mother country, and which many fear will lead to the war of the title. Meanwhile, the stepping humanoids known as trolls have begun to disappear from across the Long Earth, apparently running away from humanity after a shocking incident at a space research station. And there’s something wrong with the Old Faithful geyser on Datum Earth, which isn’t so faithful anymore.

Like its predecessor, The Long War sprawls and rambles in a fashion that generally pleases more than it frustrates, and is packed with a vast supporting cast. There’s Nelson Azikiwe, a South African minister mentioned briefly by Lobsang in the last book, who is recruited by the AI as a kind of advisor. While Joshua and Sally are trying to find out what’s happening to the trolls, a teenage prodigy named Roberta Golding accompanies a Chinese expedition across millions of Earths, becoming increasingly overwhelmed by the vast scale of it all. There are new perils as well: in addition to the friendly trolls and hostile elves, there are devious kobolds and a species of sentient dogs.

Ultimately the plots having to do with the troll disappearances and Cmdr. Kauffman’s whistle-stop tour and the war she wants to avert are less important than the exploration that occurs along the way. They’re a means by which Pratchett and Baxter interrogate humanity’s place in the universe, the way we react to the alien, and our incomplete and arrogant understanding of what constitutes sentience. There’s political and religious satire in the reactions of Datum Earth politicians and religious leaders to the implications of the Long Earth, the fallout of which began in the first book and continues here. As a result, it can be a little difficult to get too attached to any particular storyline, just because there’s so much of it, and once again the conclusions of the main plots feel a little rushed.

However, so long as you accept that the Long Earth books are really more about the journey than the destination, there is a lot to enjoy here. The characters remain engaging and the new ones are welcome additions to the cast, and the polished writing is bright with understated wit. And there is, admittedly, something very appealing, even wish-fulfilling about the idea that there could be millions of new worlds where we can try again, and not mess up the way we have here on the Datum. But Pratchett and Baxter are ever at pains to show us that such a scenario could never really be simple, and once again they end with a cliffhanger catastrophe on Datum Earth that will undoubtedly have profound consequences across the many worlds of the Long Earth. We can all eagerly look forward to the next installment of this excellent, intelligent series.